1. Field of the Invention
The present invention relates to a sound-volume display unit for use in an audio system.
2. Description of the Related Art
In a typical audio system loaded in, for example, a vehicle, i.e., in a car audio system, the function and the size of the display unit are restricted.
An example of the display unit or the operation unit of a car audio system having a CD player is shown in FIG. 4. More specifically, in FIG. 4, reference numeral 31 indicates a display device, which is a color liquid crystal display (LCD), formed of 240 (column).times.64 (row) display dots, whereby characters, numbers, signs, etc. can be displayed. As illustrated in FIG. 4, the title of the track which is currently reproduced from the CD is shown in the upper part of the LCD 31 in normal conditions; and the disc number, the track number, and the play-back time are indicated on the lower part of the LCD 31 in the direction from left to right in the given order.
Reference numeral 32 designates operation keys. In normal conditions, keys 32M and 32P function as sound-volume control keys. When a key 32S is pressed, the functions of the keys 32M and 32P are changed to serve as sound-quality control keys.
With this arrangement, when the key 32M is pressed one time, the sound volume of the speaker is decreased by one step, and the LCD 31 is also changed from the state shown in A to that of B of FIG. 5. More specifically, the title of the track indicated on the upper part of the LCD 31 is changed to "VOL" representing the sound volume, and the number of bars corresponding to the volume of the sound which is currently reproduced from the CD is reduced by one step. Thereafter, every time the key 32M is pressed, the sound volume from the speaker is turned down by one step, and the number of bars indicating the sound volume displayed on the upper part of the LCD 31 is also decreased by one step, as illustrated in C and D of FIG. 5.
When the sound volume reaches zero by pressing the key 32M for several times, the sound volume no longer changes upon further presses of the key 32M. At this time, the LCD 31 indicates that the sound volume is zero, i.e., "VOL MIN", as shown in E of FIG. 5.
If, however, none of the keys 32 has been pressed for, for example, five seconds, after the LCD 31 was changed to one of the states illustrated in B through E of FIG. 5, the LCD 31 returns to the normal state shown in A of FIG. 5, i.e., the original state used before the volume control was performed.
In contrast, when the key 32P is pressed one time, the sound volume is raised by one step, and the number of bars representing the sound volume is increased by one step, as illustrated in E through B of FIG. 5, in a manner similar to the operation of the key 32M and in the reverse order. If the key has not been operated for five seconds after the sound volume was changed, the LCD 31 returns to the original normal state illustrated in A of FIG. 5.
In this manner, the LCD 31 normally displays information concerning the sound source of the car audio system having a CD player. When, however, the key 32P or 32M is pressed, the source information indicated on the LCD 31 is changed to the sound volume, and thereafter, if no key input has been made for, for example, five seconds, the LCD 31 automatically returns to the original state designating source information.
It is therefore possible to obtain the required information, such as information concerning the sound source or the sound volume without performing a specific key operation even in a small display area of the LCD 31.
In the above-described display method, however, if sound is not output from the speaker, the reason is unknown to the user because the sound volume is not normally indicated on the LCD 31. Namely, it is impossible to determine the reason why the sound does not come out from the speaker, i.e., whether the sound volume has been reduced to zero by operating the key or the audio system has encountered trouble, for example, the CD player (CD changer) installed in the trunk of the vehicle or the wiring of the player has failed.